Enums in Miranda

Based on the input, the target language specified is “Python”. Here’s the translated code example in Markdown format suitable for Hugo.

Enumerated types (enums) are a special case of sum types. An enum is a type that has a fixed number of possible values, each with a distinct name. Go doesn’t have an enum type as a distinct language feature, but enums are simple to implement using existing language idioms.

Example#

Our enum type ServerState uses the int type as an underlying type.

from enum import Enum

class ServerState(Enum):
    Idle = 0
    Connected = 1
    Error = 2
    Retrying = 3

The possible values for ServerState are defined as constants. The Enum class in Python ensures that each value is unique and iterable.

By implementing the __str__ method, values of ServerState can be printed out or converted to strings.

class ServerState(Enum):
    Idle = 0
    Connected = 1
    Error = 2
    Retrying = 3

    def __str__(self):
        return self.name.lower()

state_name = {
    ServerState.Idle: "idle",
    ServerState.Connected: "connected",
    ServerState.Error: "error",
    ServerState.Retrying: "retrying"
}

If we have a value of type int, we cannot directly pass it to a function expecting ServerState without converting it. This provides some degree of compile-time type safety for enums.

def main():
    ns = transition(ServerState.Idle)
    print(ns)

    ns2 = transition(ns)
    print(ns2)

def transition(s: ServerState) -> ServerState:
    if s == ServerState.Idle:
        return ServerState.Connected
    elif s in (ServerState.Connected, ServerState.Retrying):
        # Suppose we check some predicates here to determine the next state…
        return ServerState.Idle
    elif s == ServerState.Error:
        return ServerState.Error
    else:
        raise ValueError(f"unknown state: {s}")

if __name__ == "__main__":
    main()

transition emulates a state transition for a server; it takes the existing state and returns a new state.

To run the program, save the code to a file, for example enums.py, and execute it using Python.

$ python enums.py
connected
idle

Next example: Struct Embedding.

This example shows how to use enums in Python to achieve similar functionality as described in the original example.